Abstract
Many run-off river types and small hydropower stations use Cross-flow turbines because of their excellent partial load characteristics and low manufacturing cost. But the maximum turbine efficiency is not high, so there have been many studies to improve the turbine performance. The authors have been developing a new shape cross-flow turbine with a cylindrical cavity and a guide wall to enhance the performance by controlling the runner outflow. Previous research has shown that the cavity effectively reduces pressure fluctuation at the nozzle's bottom tip and improves turbine efficiency. However, the mechanism is not fully understood. Therefore, the purpose of this study is to elucidate the mechanism of the cavity. The authors investigate how the flow pattern and turbine performance change with the flow pattern inside the cavity. It is clarified that the swirling flow in the cavity improves the turbine efficiency and suppresses pressure fluctuations at the lower end of the nozzle.
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